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2019 GLC300 9G-Tronic Transmission Rough Shifting & Hesitation

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Chris P. · rep 0 · May 25, 3:09 AM · 1 replies · solved · Question

Vehicle: 2019 Mercedes-Benz GLC300 4MATIC

Hey fellow Mercedes owners, I'm experiencing some concerning transmission behavior in my 2019 Mercedes-Benz GLC300 (X253) with the 9G-Tronic automatic transmission. Specifically, I'm getting rough shifts, especially noticeable at lower speeds and during downshifts (e.g., coming to a stop or accelerating from a slow roll).

Sometimes it feels like it hesitates before engaging a gear, and there's an occasional jerk that's quite unsettling. It's not constant, but frequent enough to be annoying and make me worry about long-term reliability. The car has about 45,000 miles.

Is this a known characteristic of the 9G-Tronic, or could it be a developing problem? Are there any TSBs or recalls related to this? What should I tell the dealership when I take it in? Thanks for any advice!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:09 AM

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ClearTheCode admin answer:

Rough shifting and hesitation in the 9G-Tronic transmission of your 2019 GLC300 are issues that sometimes arise, though the 9G-Tronic is generally a robust unit. Here's what you should know:

  1. Potential Causes:

    • Software Adaptation: The 9G-Tronic transmission is highly adaptive. Sometimes, its adaptation values can become skewed, leading to less smooth shifts. A simple software reset and re-adaptation can often resolve this.
    • Transmission Fluid Level/Quality: Incorrect fluid levels or degraded fluid quality can impact shift performance. While less common at 45k miles, it's a possibility.
    • Valve Body Issues: The valve body, which controls hydraulic pressure to engage gears, can sometimes develop issues, leading to rough or delayed shifts.
    • Conductor Plate/Sensor Faults: Internal sensors or the conductor plate within the transmission can fail, sending incorrect signals to the Transmission Control Unit (TCU).
    • Mechatronic Unit: In more severe cases, the mechatronic unit (which integrates the TCU and valve body) might be faulty.

  2. Known TSBs and Recalls: Mercedes-Benz has released various software updates for the 9G-Tronic transmission over the years to improve shift quality and address specific operational characteristics. It's worth checking if your vehicle is eligible for any such updates.

  3. When to See a Shop: You should take your GLC300 to a Mercedes-Benz dealership or a transmission specialist promptly. While some rough shifting can be 'normal' during adaptation, persistent or worsening symptoms indicate a need for professional diagnosis. Ignoring transmission issues can lead to more significant and costly repairs down the line.

  4. What to Expect at the Shop:

    • Diagnostic Scan: They will connect to the vehicle's diagnostic port to check for any stored fault codes (e.g., P0731 for incorrect gear 1 ratio, P0732 for incorrect gear 2 ratio, or Mercedes-specific codes related to the TCU). These codes are crucial for pinpointing the problem.
    • Software Update/Adaptation Reset: The first step will likely be checking for and applying any available software updates for the TCU and performing a transmission adaptation reset.
    • Fluid Check: They will inspect the transmission fluid level and condition.
    • Further Diagnostics: If software fixes don't work, they will perform more in-depth diagnostics, potentially involving pressure tests or internal component checks.

  5. Recommendation: Clearly describe the symptoms to the technician, including when they occur (e.g., specific gears, hot/cold engine, acceleration/deceleration). This information is invaluable for accurate diagnosis.

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